Braeu, an internationally known expert on conifers, searches the forest for a slow-growing mass of branches called a witch's broom.

"It has nothing to do with being a witch," Braeu told The Janesville Gazette .

He hunts the odd-looking distortion in trees, usually with fellow plant lovers, and they use the "brooms" to develop dwarf conifers.

You can see some of the conifers at Braeu's Janesville home, where he has filled his corner lot with plant varieties propagated by himself and friends in the United States and around the world.

Some plants are tucked among leaves in a deer-proof enclosure.

Others show off their colors and cascading forms in various beds hugging his home.

They all share one thing in common: None would exist without the help of a witch's broom.

In fact, brooms are the genetic source of many dwarf conifers sold at nurseries.

Here's how it works:

When Braeu finds a broom, he skillfully grafts a piece of it to the stem and roots of another tree of the same kind. If the broom has been caused by a genetic mutation, the resulting plant will grow slowly and compactly like the mother broom.

Braeu has created many new varieties, mostly conifers, using brooms from spruce, firs, pines and other trees.

Gardeners appreciate the dwarf varieties, which rarely outgrow their places in home landscapes.

Braeu especially loves conifers because they are always green.

"They always look alive in the wintertime," he said.

Joe Braeu and his wife, Debbie, owned and operated a specialty landscape nursery outside Duluth, Minnesota, before moving to Janesville more than a year ago.

Joe Braeu learned about horticulture in his native Germany.

Debbie Braeu, who was trained as a dental assistant, learned the nursery and landscaping business from the ground up.

On the road, Debbie Braeu does most of the driving.

"I tell everyone I drive because Joe is always looking up in trees," Debbie Braeu said.

Joe Braeu keeps the locations of up to 900 witch's brooms, mostly in the Midwest and Ontario, on his GPS.

"Wherever I travel, I spot these things," he said.

The best time of the year to look for brooms is after the leaves have fallen.

Ideally, Joe Braeu searches for brooms low in the tree so he can knock down pieces or reach them with a saw.

He carries a long pole, a saw and ax and a .22-caliber rifle. If all else fails, he shoots the broom out of the tree. Things don't always go well.

Joe Braeu told the story of a broom 40 feet high in a tamarack tree in the wilds of northern Minnesota.

"Everything wrong happened that could," he recalled.

He pushed his 40-foot pole through the tamarack limbs until the top section of the pole broke off and crashed down.

That's when he shot the broom with his rifle and brought it down only a foot.

Eventually, Joe Braeu found an alder branch and squeezed it into the hole of his broken pole.

Then, he wove the pole back through the branches and managed to topple the broom.

"I used all my ingenuity," Joe Braeu said, smiling.

Propagating a new species gives him naming rights, and he has named several trees after family members. Sometimes, he chooses a name that reflects a plant's origin.

Debbie Braeu told the story of one planted they called "Highway Patrol."

"We were once on an interstate, and I was waiting as Joe checked out a broom in a red pine," Debbie Braeu said. "I looked up, and there was a highway patrol pulling up behind me."

The officer informed her that stopping on a freeway is dangerous and should be done only in emergencies.

After moving to Janesville, Joe and Debbie Braeu did not take long to get involved at Rotary Gardens.

"Their collective plant knowledge has been extremely helpful at the gardens," said Mark Dwyer, director of horticulture. "They have a long history of growing and promoting a wide range of plants for the Midwest and understand our challenges."

At 73, Joe Braeu cannot see a time when he will give up broom hunting.

"I will have to be dead to stop creating plants," he said. "I don't do this just for me but for everyone out there."